Lecture 20: Blood Vessels Flashcards Preview

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Flashcards in Lecture 20: Blood Vessels Deck (22):

Describe the three kinds of vessels found in the body and give their function

Arteries: carries blood away from the heart; oxygenated except for pulmonary circulation and umbilical vessels of fetid
Capillaries: contact tissue cells and directly serve cellular needs
Veins: carry deoxygenated blood towards the heart


Structure of blood vessel walls:
Arteries and veins

Arteries and veins:
-Tunica intima: endothelium lines the lumen of all vessels
-Tunica media: smooth muscle and sheets of elastin.
-Tunica externa: collagen fibres protect and reinforce
Lumen: central blood containing space
Capillaries: endothelium of one cell thickness
Refer to slide 6 for image


Elastic arteries:

-Large thick walled arteries with elastin in all three tunics
-aorta and its major branches
-large lumen offers low resistance
-acts as pressure reservoirs- expand and recoil as blood is ejected from the heart


Muscular arteries and arterioles

-Distal to elastic arteries; deliver blood to body grabs
-have thick tunica media with more smooth muscle
-arterioles: smallest arteries and lead to capillary beds



Microscopic blood vessels
-walls of thin tunica intima, only one cell thick
-size of lumen allow only a single red blood cell to pass at a time
-found in all tissues except for cartilage, epithelia, cornea and lens of eye
-functions: exchange of gases, nutrients, wastes, hormones etc


What are the three structural types of capillaries?

1. Continuous capillaries: tight junctions connect endothelial cells: in blood brain barrier.
-intercellular clefts allow for passage of fluids and small solutes
2. Fenestrated capillaries:
-some endothelial cells contain pores (fenestrations)
-more permeable than continuous capillaries
-function in absorption or filtrate formation (small intestine, endocrine glands and kidneys)
3. Sinusoidal capillaries:
-fewer tight junctions, larger intercellular clefts, larger lumens
-allow large molecules and blood cells to pass between blood and surrounding tissue
-found in liver, bone marrow and spleen
Refer to slides 13-15 for pictures



-Formed when capillary beds unite
-very porous; allow fluid and WBCs into tissues
-larger venules have one or two layers of smooth muscle cells



-formed when venules converge
-have thinner walls, larger lumen compared with arteries
-blood pressure is lower than in arteries
-thin tunica media and thick tunica externa consisting of collagen fibres and elastic networks
-blood reservoirs; contain about 60% of the blood volume


What are the veins adaptions that ensure return of blood to he heart?

1. Large diameter lumens offer little resistance
2. Valve prevents backfow of blood
-most abundant in veins of the limbs
Venous sinuses: flattened veins with extremely thin walls eg coronary sinus of the heart and dural sinuses of the brain)


Vascular anastomoses:

-interconnections of blood vessels
Arterial anastomoses provide alternative pathways to a given body region
-common at joints, in abdominal organs, brain, and heart
Vascular shunts of capillaries shunts of capillaries are examples of arteriovenous anastomoses
-venous anastomoses are common


Factors aiding in venous return

1. Respiratory pump: pressure changes created during breathing moves blood towards the heart be squeezing abdominal veins as thoracic veins expand
2. Muscular pump: contraction of skeletal muscles "milk" blood toward the heart and valves prevents backfow


The Vasomotor centre

A cluster of sympathetic neurons in the medulla oblongata that oversee changes in blood vessel diameter
-part of the cardiovascular centre
Receives input from:
-baroreceptors: walls of large arteries of the neck and thorax ie carotid and aorta
-chemoreceptors: large arteries of neck ie carotid and aorta, chemoreceptors respond mainly to rise in CO2


Short term mechanisms: hormonal control

Adrenal medulla hormones:
-angiotensin 2
Posterior pituitary:
-antidiuretic hormone (vasopressin)


Monitoring circulatory efficiency:

Vital signs: pulse and blood pressure, along with respiratory rate and body temperature
Pulse: pressure wave caused by the expansion and recoil of arteries
Need to identify the following pulses:
-radial pulse
-ulnar pulse
-carotid pulse
-brachial pulse
-femoral pulse
-dorsal pedal pulse
-posterior tibia pulse


Systemic blood pressure:

The pumping action of the heart generates blood flow
-pressure results when flow is opposed by resistance of the arterial wall
Systemic pressure:
-is highest in the aorta
-declines throughout the pathway
-is 0mm Hg in the right atrium


Arterial blood pressure:

Reflects two factors of the arteries close to the heart
-volume of blood forced into them at any time
Systolic pressure: pressure exerted during ventricular contraction
Diastolic pressure: lowest level of arterial pressure


Blood flow: brain

Blood flow to the brain is constant, as neurons are intolerant of ischemia
-capillaries have tight junctions and are continuous, thus protective as the blood: brain barrier


Blood flow: skin

Blood flow through the skin:
-supplies nutrients to cells
-helps maintain body temperature
-provides a blood reservoir
-is controlled by sympathetic nervous system reflexes, initiated by temperature receptors and the central nervous system


Temperature regulation

As temperature rises
-hypothalmic signals reduce vasomotor stimulation of the skin vessels
-heat radiates from the skin
-sweat also causes vasodilation

As temperature decreases, blood is shunted to deeper, more vital organs


Blood flow: lungs

Pulmonary circuit is unusual in that:
-the pathway is short
-arteries/ arterioles are more like veins/ venules (thin walled, with large lumens)
-arterial resistance and pressure is low


Blood flow: heart
During ventricular systole
During strenuous exercise

During ventricular systole:
-coronary vessels are compressed
-myocardial blood flow ceases
During strenuous exercise
-coronary vessels dilate
-blood flow may increase


Differences between arteries and veins: